Chromium (Cr)
Element 24 · Transition metal · Solid at 25 °C · Group 6, Period 4
Chromium puts the mirror shine on chrome plating and the “stainless” in stainless steel. Trace chromium colors rubies red and emeralds green.
On the periodic table, chromium sits in group 6 in period 4. It is one of 38 elements classified as a transition metal, and at room temperature (25 °C) it is a solid.
Transition metals occupy the wide d-block in the middle of the table. As a family they are hard, dense, high-melting metals that conduct heat and electricity well. Their partly filled d-orbitals let many of them take several oxidation states, form vividly colored compounds, and act as catalysts — which is why so much of industry, and so much of biology, runs on this block.
Properties of chromium
| Atomic number (Z) | 24 |
|---|---|
| Symbol | Cr |
| Atomic mass | 51.996 |
| Category | Transition metal |
| Group | 6 |
| Period | 4 |
| Block | d-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Ar] 3d5 4s1 |
| Electronegativity (Pauling) | 1.66 |
| Melting point | 1,907 °C (2,180.15 K / 3,464.6 °F) |
| Boiling point | 2,671 °C (2,944.15 K / 4,839.8 °F) |
| Density | 7.15 g/cm³ |
Position in the periodic table
Chromium shares group 6 with Molybdenum (Mo), Tungsten (W), Seaborgium (Sg). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Physical properties
Chromium melts at 1,907 °C (2,180.15 K / 3,464.6 °F) and boils at 2,671 °C (2,944.15 K / 4,839.8 °F), giving it a liquid range of about 764 °C at standard pressure.
Its density is 7.15 g/cm³.
See also: the interactive periodic table, how to read the periodic table, periodic trends.